Production of c6 cyclic hydrocarbons



United States Patent 3,272,878 PRODUCTION OF C CYCLlC HYDROCARBONS John T. Cabbage, Bartlesville, Okla, assignor to Phillips Petroleum Company, a corporation of Delaware Filed Apr. 7, 1964, Ser. No. 357,888 4 Claims. (Cl. 260-666) This invention relates to a process and apparatus for producing C cyclic hydrocarbons from a mixture of hydrocarbons.

In the production of high purity benzene and cyclohexane, it is desirable to concentrate the benzene and cyclohexane formers-methylcyclopentane, cyclohexane and benzene-from a straight run or natural gasoline fraction. These cyclohexane and benzene formers (C cyclic hydrocarbons) normally occur in relatively small concentrations with large concentrations of isoand normal C and C hydrocarbons. A reasonable recovery of these cyclohexane and benzene formers (above 25-35 percent) is normally impractical due to the precise fractionation required, as evidenced by the following table presenting the constituents of a straight run gasoline fraction and their boiling points:

Dimethylcyclopentanes 195 .4l97.4

3 -methylhexane 197.5 3-ethylpentane 200.2 Normal heptane 209.2

It can readily be seen from the above table that 0 and heavier hydrocarbons with the exception of 2,2-dimethylpentane and 2,4-dimethylpentane, which normally occur in small concentrations, can be separated by fractionation in the recovery of the C cyclic hydrocarbons but normal hexane cannot be separated without excessive losses of methylcyclopentane and benzene.

Accordingly, an object of my invention is to provide an improved process and apparatus for the production of C cyclic hydrocarbons.

Another object of my invention is to provide a process and apparatus for the recovery of methylcyclopentane, cyclohexane and benzene from a C -C hydrocarbon mixture.

Other objects, advantages and features of my invention Will be readily apparent to those skilled in the art from the following description, the drawing and appended claims.

By my invention, a hydrocarbon mixture is fractionated to recover therefrom an intermediate C C boiling fraction containing C cyclic hydrocarbons; the said intermediate boiling fraction is subjected to an isomerization process step wherein the normal hexane and low boiling C hydrocarbons contained therein are isomerized; and the isomerization zone efiluent is separated by a series of fractionation steps to recover therefrom a concentrated C cyclic hydrocarbon fraction. The invention is broadly applicable to the recovery of the C cyclic hydrocarbons,

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methylcyclopentane, benzene and cyclohexane from hydrocarbon mixtures. The term C cyclic hydrocarbon fraction as hereinafter employed refers to a hydrocarbon fraction containing benzene and at least one of the remaining C cyclic hydrocarbons methylcyclopentane and cyclohexane.

The drawing is a schematic representation of one embodiment of the invention.

A better understanding of the invention can be obtained by referring to the drawing and the following description of the invention as applied to the recovery of C cyclic hydrocarbons from a straight run gasoline fraction. A straight run gasoline fraction comprising C -C hydrocarbons and containing minor amounts of isobutane, normal butane, isopentane and heavy residual hydrocarbons is passed via conduit means 10 to a distillation (dehexanizer) column 11. Within distillation column 11, hydrocarbons heavier than cyclohexane (3,3-dimethylpentane and heavier) are separated from the hydrocarbon feed mixture and withdrawn from distillation column 11 via conduit means 12. The remainder of the hydrocarbon feed mixture (cyclohexane and lighter) passed to distillation column 11 is withdrawn from distillation column 11 via conduit means 13 and passed as feed to a distillation column 14. Typical operating conditions within distillation column 11 are:

Top temperature, F. 230 to 250 Top pressure, p.s.i.g 35 to 45 Bottom temperature, F 305 to 325 Bottom pressure, p.s.i.g 40 to 50 Top temperature, F 235 to 255 Top pressure, p.s.i.g 35 to 45 Bottom temperature, F. 280 to 300 Bottom pressure, p.s.i.g 40 to 55 Within isomerization zone 18, the normal hexane fraction in the hydrocarbon feed to the isomerization zone is isomerized to isohexane and the lighter isoheptanes contained in the said feed are isomerized to higher boiling isomers, including normal heptane. Within isomerization zone 18, the liquid hydrocarbon feed is contacted with a conventional isomerization catalyst such as a chloridepromoted aluminum chloride and platinum catalyst supported on alumina or a fluoride promoted platinumalumina catalyst. When employing a platinum-alumina fluoride promoted catalyst, the temperature and pressure of the isomerization zone is preferably maintained typically in the range of 400-750 F. and in the range of 300 to 500 p.s.i.g, respectively.

An isomerization zone effluent is withdrawn from isomerization zone 18 via conduit means 19 and passed to a distillation column 20. Within (denormal hexanizer) distillation column 20, a normal hexane and lighter hydrocarbon fraction is separated from the hydrocarbon feed and withdrawn from distillation column 20 via conduit means 21. A heavier residual hydrocarbon fraction comprising methylcyclopentane, benzene, cyclohexane and heavier hydrocarbons, including the above-produced heavier heptane isomers, is withdrawn from distillation column 20 via conduit means 22 and passed to (decyclohexanizer) distillation column 23. Typical operating conditions within distillation column 20 are:

Top temperature, F 215 to 235 Top pressure, p.s.i.g 30 to 40 Bottom temperature, F 245 to 265 Bottom pressure, p.s.i.g 35 to 45 It is within the scope of this invention to recycle the hydrocarbon fraction withdrawn from distillation column 20 via conduit means 21 to the distillation column feed via conduit means 24, thereby recovering via distillation column 14 and isomerization zone 18 any methylcyclopentane and any normal hexane withdrawn from distillation column 20 via conduit means 21.

Within distillation column 23, the hydrocarbon feed is separated into a product fraction comprising methylcyclopentane, benzene and cyclohexane and a residual hydrocarbon fraction comprising the produced heavier isoheptanes and normal heptane. The product fraction is withdrawn from distillation column 23 via conduit means 26. The residual hydrocarbon fraction is withdrawn from distillation column 23 via conduit means 27. The residual hydrocarbon fraction withdrawn from distillation column 23 can be combined with the residual hydrocarbon fraction withdrawn from distillation column 11 as herein illustrated. Typical operating conditions within distillation column 23 are:

Bottom pressure, p.s.i.g 35 to 45 The product fraction in conduit 26 comprising 60-90 weight percent C cyclic hydrocarbons can be passed to subsequent process steps, not herein illustrated. The product fraction can be passed to a reforming step to yield benzene or to hydrogenation and isomerization process steps to yield cyclohexane or methylcyclopentane.

It is considered to be within the skill of the art to provide means for heating and refluxing columns 11, 14, 20 and 23 and to provide conventional means of fluid transmission and process control, not herein illustrated. It is also considered to be within the skill of the art to provide means for heating and cooling process streams. Such heating and cooling means except Where herein illustrated are considered to be conventional and within the skill of the art.

The following example illustrates operation in accordance with the invention utilizing the flow of the drawing to produce a product stream having a concentration of benzene and cyclohexane formers of 60-90 weight percent purity.

EXAMPLE Distillation Column Column Column Column Column Conditions 14 20 23 Top Temperature, F 240 245 224 250 Top Pressure, p.s.i.g 42 40 35 35 0 Bottom Temperature, 315 289 254 300 Bottom Pressure, p.s.i.g 47 49 41 40 Isomerization conditions Pressure, p.s.i.g 575 Temperature, F 700 Catalyst-Platinum, 0.36 weight percent, fluoride, 2.8 weight percent, on alumina (percentages based on total catalyst). 7

The composition (barrels per day) of the hydrocarbon feed to distillation column 11, the composition of the product fraction Withdrawn via conduit means 26, the composition of the charge to isomerization via conduit means 17, and other streams in barrels per day, are as follows:

Component 10 13 16 17 19 C5 and lighter 160 160 I06 2,216 2, 216 1,773 443 2, 231 41 5s MCP- 2,2 and 2,4-DMP. BZ CvCa Other 101 and N01. C1300 E.P

Stream 21 22 27 20 440 474 1,794 43 285 CV00 264 11 253 Other I01 and NC1 324 322 2 The product stream recovered from distillation column 23 via conduit 26 contains 70.7 volume percent of C cyclic hydrocarbons.

As will be evident to those skilled in the art, various modifications of this invention can be made, or followed, in the light of the foregoing disclosure, without departing from the spirit or scope thereof.

I claim:

1. A process which comprises passing a hydrocarbon mixture to a first distillation zone, said hydrocarbon mixture comprising isohexane and lighter materials, normal hexane, methylcyclopentane, 2,2-dimethylpentane, 2,4-dimethylpentane, benzene, cyclohexane and materials heavier than cyclohexane; withdrawing from said first distillation zone a residual hydrocarbon fraction containing hydrocarbons heavier than cyclohexane; passing the remainder of said hydrocarbon mixture containing cyclohexane and materials lighter than cyclohexane from the upper region of said first distillation zone to a second distillation zone; withdrawing from said second distillation zone an overhead stream containing isohexane and lighter hydrocarbons; withdrawing from said second distillation zone a first bottoms stream containing 2,2-dimethylpentane, 2,4-dimethylpentane, benzene, cyclohexane, substantially all of the methylcyclopentane contained in said hydrocarbon mixture and a major portion of normal hexane contained in said hydrocarbon mixture; passing the thus withdrawn first bottoms stream into an isomerization zone containing a catalyst consisting of fluoride promoted platinum-alumina; maintaining the temperature and pressure in said isomerization zone in the ranges of 400 to 750 F. and 300 to 500 -p.s.i.g., respectively, to isomerize: normal hexane in the hydrocarbon feed to said isomerization zone to isohexane; 2,2-dimethylpentane and 2,4-dimethylpentane in the hydrocarbon feed to said isomerization zone to higher boiling isoheptanes; and cyclohexane in the hydrocarbon feed to said isomerization zone to methylcyclopentane; passing the efiluent from said isomerization zone to a third distillation zone; withdrawing from said third distillation zone an overhead stream containing hydrocarbons lighter than normal hexane and a minor amount of the normal hexane contained in said isomerization zone efiluent; withdrawing from said third distillation zone a second bottoms stream containing methylcyclopentane, benzene, cyclohexane and heavier hydrocarbons and a major portion of the normal hexane contained in said isomerization zone efiluent; passing the thus withdrawn second bottoms stream into a fourth distillation zone; withdrawing from said fourth distillation zone an overhead product containing substantially all of the normal hexane contained in said second bottoms stream and at least 60 volume percent cyclic C hydromixture passed to said first distillation zone comprises a straight run gasoline fraction.

References Cited by the Examiner UNITED STATES PATENTS 2,382,446 8/1945 Ross et a1 260666 2,505,792 5/1950 Ross et al 260-666 2,953,606 9/1960 Dean et a1. 260-666 3,078,323 2/1963 Kline et al. 260-683.78

DELBERT E. GANTZ, Primary Examiner.

V. OKEEFE, Assistant Examiner. 

1. A PROCESS WHICH COMPRISES PASSING A HYDROCARBON MIXTURE TO A FIRST DISTILLATION ZONE, SAID HYDROCARBON MIXTURE COMPRISING ISOHEXANE AND LIGHTER MATERIALS, NORMAL HEXANE, METHYLCYCLOPENTANE, 2,2-DIMETHYLPENTANE, 2,4-DIMETHYLPENTANE, BENZENE, CYCLOHEXANE AND MATERIALS HEAVIER THAN CYCLOHEXANE; WITHDRAWING FROM SAID FIRST DISTILLATION ZONE A RESIDUAL HYDROCARBON FRACTION CONTAINING HYDROCARBONS HEAVIER THAN CYCLOHEXANE; PASSING THE REMAINDER OF SAID HYDROCARBON MIXTURE CONTAINING CYCLOHEXANE AND MATERIALS LIGHTER THAN CYCLOHEXANE FROM THE UPPER REGION OF SAID FIRST DISTILLATION ZONE TO A SECOND DISTILLATION ZONE; WITHDRAWING FROM SAID SECOND DISTILLATION ZONE AN OVERHEAD STREAM CONTAINING ISOHEXANE AND LIGHTER HYDROCARBONS; WITHDRAWING FROM SAID SECOND DISTILLATION ZONE A FIRST BOTTOMS STREAM CONTAINING 2,2-DIMETHYLPENTANE, 2,4-DIMETHYLPENTANE, BENZENE, CYCLOHEXANE, SUBSTANTIALLY ALL OF THE METHYLCYCLOPENTANE CONTAINED IN SAID HYDROCARBON MIXTURE AND A MAJOR PORTION OF NORMAL HEXANE CONTAINED IN SAID HYDOCARBON MIXTURE; PASSING THE THUS WITHDRAWN FIRST BOTTOMS STREAM INTO AN ISOMERIZATION ZONE CONTAINING A CATALYST CONSISTING OF FLUORIDE PROMOTED PLATINUM-ALUMINA; MAINTAINING THE TEMPERATURE AND PRESSURE IN SAID ISOMERIZATION ZONE IN THE RANGES OF 400 TO 750*F. AND 300 TO 500 P.S.I.G., RESPECTIVELY, TO ISOMERIZE: NORMAL HEXANE IN THE HYDROCARBON FEED TO SAID ISOMERIZATION ZONE TO ISOHEXANE; 2,2-DIMETHYLPENTANE AND 2,4-DIMETHYLPENTANE IN THE HYDROCARBON FEED TO SAID ISOMERIZATION ZONE TO HIGHER BOILING ISOHEPTANES; AND CYCLOHEXANE IN THE HYDROCARBON FEED TO SAID ISOMERIZATION ZONE TO METHYLCYCLOPENTANE; PASSING THE EFFLUENT FROM SAID ISOMERIZATION ZONE TO A THIRD DISTILLATION ZONE; WITHDRAWING FROM SAID THIRD DISTILLATION ZONE AN OVERHEAD STREAM CONTAINING HYDROCARBONS LIGHTER THAN NORMAL HEXANE AND A MINOR AMOUNT OF THE NORMAL HEXANE CONTAINED IN SAID ISOMERIZATION ZONE EFFUENT; WITHDRAWING FROM SAID THIRD DISTILLATION ZONE A SECOND BOTTOMS STREAM CONTAINING METHYLCYCLOPENTANE, BENZENE, CYCLOHEXANE AND HEAVIER HYDROCARBONS AND A MAJOR PORTION OF THE NORMAL HEXANE CONTAINED IN SAID ISOMERIZATION ZONE EFFLUENT; PASSING THE THUS WITHDRAWN SECOND BOTTOMS STREAM INTO A FOURTH DISTILLATION ZONE; WITHDRAWING FROM SAID FOURTH DISTILLATION ZONE AN OVERHEAD PRODUCT CONTAINING SUBSTANTIALLY ALL OF THE NORMAL HEXANE CONTAINED IN SAID SECOND BOTTOMS STREAM AND AT LEAST 60 COLUME PERCENT CYCLIC C6 HYDROCARBONS, AND WITHDRAWING ISOHEPTANE AND HEAVIER HYDROCARBONS FROM THE LOWER REGION OF SAID FOURTH DISTILLATION ZONE. 